<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<style>
#invalid1 { background-image: url(""); }
#invalid2 { background-image: url("#123"); }
</style>
</head>
<body>
<blockquote id="invalid1">invalid1</blockquote>
<blockquote id="invalid2">invalid2</blockquote>
</body>
</html>
